The present invention relates generally to semiconductor fabrication and more specifically to alignment marks and semiconductor etching at tiny areas.
Alignment marks are used to permit precise alignment of photolithographic masks with the wafer during masking steps to minimize misalignment between multiple layers. However, the alignment marks are xe2x80x98blindedxe2x80x99 after non-ODR shallow trench isolation (STI) chemical mechanical polishing (CMP) processes. This prevents transfer of the lower alignment mark to the next, upper layer, for example a metal layer.
An additional photolithography and etching step (ODR) are required to clear out the silicon oxide residue from the xe2x80x98blindedxe2x80x99 alignment mark field. This increases costs, increases the cycle time and manufacture loading. Further, the ODR approach is limited by the circuit design rule especially as the design rule passes 0.1 xcexcm logic and beyond.
Blind alignment marks will become a critical issue in non-OD reverse tone photo/etch (ODR) processes after 0.1 xcexcm and beyond shallow trench isolation (STI) CMP.
U.S. Pat. No. 6,194,287 B1 to Jang et al. describes an STI process and reverse mask to clear off alignment marks.
U.S. Pat. No. 6,080,635 to Jang et al. describes discloses a method to preserve alignment marks with STI processes.
U.S. Pat. No. 6,043,133 to Jang et al. describes a process to improve STI removal over alignment marks.
U.S. Pat. No. 6,015,744 to Tseng describes a clear out and alignment mark process.
U.S. Pat. No. 5,188,258 to Iwashita describes a quantitative fluid discharge device.
Accordingly, it is an object of one or more embodiments of the present invention to provide an improved method of unblinding alignment marks.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a substrate having a cell area and an alignment mark area is provided. The substrate having an alignment mark within the alignment mark area. An STI trench is formed into the substrate within the cell area. A silicon oxide layer is formed over the substrate, filling the STI trench and the alignment mark. The silicon oxide layer is planarized to form a planarized STI within the STI trench and leaving silicon oxide within the alignment mark to form a blinded alignment mark. A wet chemical etchant is applied within the alignment mark area over the blinded alignment mark to at least partially remove the silicon oxide within the alignment mark. The remaining silicon oxide is removed from within the blinded alignment mark to unblind the alignment mark. A drop etcher apparatus is also disclosed.